Real time digital pulse shaping techniques allow synthesis of pulse shapes that have been difficult to realize using the traditional analog methods. Using real time digital shapers, triangular/trapezoidal filters can be synthesized in real time, as described in V. T. Jordanov et al., Nucl. Instr. and Meth., A353, pg. 261 (1994), or in quasi real time, as described in G. Ripamonti et al., Nucl. Instr. and Meth., A340, pg. 584 (1994). These filters exhibit digital control on the rise time, fall time, and flattop of the trapezoidal shape. Thus, the trapezoidal shape can be adjusted for optimum performance at different distributions of the series and parallel noise.
The trapezoidal weighting function (WF) represents the optimum time-limited pulse shape when only parallel and series noises are present in the detector system. See, V. Radeka, IEEE Trans. Nucl. Sci., NS-15, pg. 455 (1968); F. S. Goulding, Nucl. Instr. and Meth., A100, pg. 493 (1972); and E. Gatti and M. Sampeitro, Nucl. Instr. and Meth., A287, pg 513 (1990). In the presence of 1/f noise, the optimum WF changes depending on the 1/f noise contribution. Optimum pulse shapes have been derived, as described in E. Gatti and M Sampietro, ibid., and E. Gatti, et al., Nucl. Instr. and Meth., A394, pg. 268 (1997), for both cases of 1/f voltage and 1/f current noise sources. These shapes can be synthesized using intensive off-line computational techniques that reduce significantly the throughput of the spectroscopy system.
Accordingly, it is a principal object of the invention to provide a method of real time digital pulse shaping with variable weighting function.
It is a further object of the invention to provide such a method that can be used for both cases of 1/f voltage and 1/f current noise sources.
Other objects of the invention, as well as particular features and advantages thereof, will be apparent or be elucidated in the following description and the accompanying drawing figures.